Isochron

Code for fitting isochrons on uranium-thorium-lead (U-Th-Pb) isotope data. A technical consequence of measuring multiple isotopes of the same element is that the associated errors are highly corellated. The U-Th-Pb isotope systems consists of three coupled decay systems: ²³⁸U to ²⁰⁶Pb, ²³⁵U to ²⁰⁷Pb and ²³²Th to ²⁰⁸Pb. Therefore to obtain the highest amount of geochronological information, multiple lead isotopes are measured in parallel.

Error ellipses

In order to graphically convey error corellation in the isotope data, error ellipses must be constructed from measured coordinates in isotope ratio space, the measurement error on each isotope ratio, and the associated error corellation. This code calculates the proper coordinates for the error ellipse (default 95% confidence interval). In addition, there is a function to calculate the ‘best fit’ distance to a fitted isochron, to evaluate the misfit of each data point.

Yorkfit

Implementation of the standard isochron method emplyoed by ISOPLOT (e.g. Ludwig, 2003) as defined in York 1966, 1969 York et al. 2014. The method uses two measured variables with correlated errors.